A polyetherester copolymer has excellent flexibility and elastic recovery, thereby being used as a substitute for a conventional rubber material. In particular, a polyetherester copolymer has both characteristics of an elastic material that rubber has, and thermoplastic characteristics of an ordinary plastic material, thereby being a material widely used for an automobile part such as extrusion wire coating, a power transmission boot, a cooling water circulation tube, and the like, and for an electronic component material.
Such a polyetherester copolymer is usually prepared by transesterifying an acid component such as dicarboxylic acid and the like, diol such as butanediol and the like, and polyol such as polytetramethylene ether glycol and the like, and then by condensation polymerizing the same. The diol is used in excess compared with other raw materials during the transesterification reaction, and unreacted diol used in excess is separated out as a byproduct after the condensation polymerization reaction to be reused again as a raw material in the transesterification reaction.
At this time, the byproduct includes, in addition to the unreacted diol, various kinds of impurities generated during the reaction, for example, a low boiling point compound including a thermal decomposition product of diol, such as methanol, water, tetrahydrofuran and the like, and a high boiling point compound such as an oligomer.
The thermal decomposition product of diol such as waster, tetrahydrofuran, and the like may cause a problem of generating a bad odor in a copolymer finally prepared, or increasing the rate of a side reaction by causing the hydration of a reaction catalyst. The methanol is prepared when an acid component unconverted in the transesterification reaction is condensation polymerized, and may deteriorate the initial reactivity of the transesterification reaction. The oligomer of polyol is concentrated, and may increase the clogging of a condenser in an upper portion of a condensation polymerization reactor, and may cause a problem of deteriorating the viscosity characteristic when included in a large amount in the copolymer finally prepared. Therefore, the byproduct may cause various problems when reused intact as a reaction raw material of a transesterification reaction, thereby deteriorating the physical properties of the copolymer finically prepared, and deteriorating the productivity.
Therefore, in order to prevent the problems from occurring, it is necessary to separate and remove impurities included in a byproduct other than unreacted diol, especially a high boiling point compound, before reusing the byproduct as a reaction raw material.
Under the above circumstances, the present inventors completed the present invention capable of improving the processibility efficiency and economical efficiency of a copolymer finally prepared while not adversely affecting the physical properties thereof, by confirming that a high boiling point compound such as an oligomer of polyol which adversely affects a reaction device is included in a byproduct including unreacted diol, obtaining a recycle stream by separating and removing a low boiling point compound and a high boiling point compound included in the byproduct before reusing the byproduct, and reusing the recycle stream as a reaction raw material.